Organic polymer material, process for producing the same, and heavy-metal ion remover comprising the same

ABSTRACT

An object of the present invention is to provide a heavy metal ion scavenger having more excellent scavenging performance than previously. In order to attain this object, organic polymer materials of the present invention are characterized in that they have a polymer side chain derived from a haloalkyl-substituted styrene on the backbone of an organic polymer base and a functional group capable of forming a complex with a heavy metal ion has been introduced onto said polymer side chain. These organic polymer materials have excellent heavy metal ion scavenging performance so that they can be suitably used as heavy metal ion scavengers.

FIELD OF THE INVENTION

The present invention relates to organic polymer materials that can beused as scavengers for removing heavy metal ions such as cobalt, nickel,copper, mercury, cadmium, lead, iron, zinc or the like contained inindustrial water or wastewater in the fields of precision electronicindustry, medicine, pharmacy, nuclear power generation, etc.

PRIOR ART

Conventional water treatment techniques for removing heavy metal ionscontained in industrial water or wastewater involve (1) precipitatingtarget heavy metal ions as insoluble metal salts or hydroxides; (2)concentrating heavy metal ions by evaporation; (3) removing heavy metalions by adsorption to an adsorbent; (4) removing heavy metal ions bymembrane separation; (5) removing heavy metal ions by solventextraction; (6) electrochemically depositing heavy metal ions at anelectrode; or the like.

Method (1) above comprising precipitating heavy metal ions as hydroxidesor the like is currently most common, but this method has problems suchas difficulty in post-treatment or recovery/recycling of sludgeproduced, redissolution of amphoteric materials in treated water atexcessively higher pH, formation of complex salts that are difficult toremove, etc. As a means to solve these problems, the use of bead-likechelate resins has become common in connection with adsorptive removalmethod (3) above.

However, adsorptive method with chelate resins has also the disadvantagethat large amounts of resins are required because it is difficult toefficiently separate low levels of dissolved heavy metal ions byadsorption. Furthermore, this method is limited to applications usingpacked column systems because chelate resins are in the form of roundspheres having a diameter of about 0.2-0.8 mm. This may also cause thedisadvantage that the flow rate cannot be increased due to greatpressure loss when a stock solution is to be continuously flown.

Moreover, bead-like chelate resins normally have a rigidthree-dimensional structure due to the presence of crosslinkers such asdivinylbenzene, so that heavy metal ions or regenerants cannot diffuseinto the resins at sufficient speed. Therefore, removal speed of heavymetal ions or dissolution speed of heavy metal ions during regenerationof the resins is also low. In addition, these resins were practicallydifficult to recycle because chelate groups may be separated from theresins to diffuse or may be chemically changed under the action ofregenerants during regeneration of the resins. On the other hand, theywere difficult to incinerate when they were not recycled but desired tobe disposable. This invites the great problem of how to reduce thevolume of radioactive waste chelate resins after they are used to removeheavy metal ions in wastewater from a nuclear power plant, for example.Improper disposal of even non-radioactive waste resins may causeadsorbed heavy metal ions (eg, mercury or cadmium) to diffuse to inviteserious secondary pollution.

JP-A-187143/1990 proposes a heavy metal ion scavenger to solve the aboveproblems in which a graft polymer side chain is introduced into apolymer base by graft-polymerizing a polymerizable monomer having anepoxy group such as glycidyl methacrylate and an iminodiacetate group isimmobilized as a chelate group on the graft polymer side chain. Theheavy metal ion scavenger proposed here shows high adsorptionperformance for trace heavy metal ions in aqueous solutions.

However, there are still needs for scavengers showing further excellentheavy metal ion scavenging performance.

DISCLOSURE OF THE INVENTION

As a result of careful studies to further improve performance of heavymetal ion scavengers of the type having a polymer side chain on thebackbone of an organic polymer and a functional group capable of forminga complex with a heavy metal ion on the polymer side chain, weaccomplished the present invention on the basis of the finding that anorganic polymer material obtained by using a polymer side chain derivedfrom a styrene compound having a haloalkyl group on the benzene ring andintroducing a functional group capable of forming a complex with a heavymetal ion onto the polymer side chain shows more excellent heavy metalion scavenging performance than conventional heavy metal ion scavengers.

Accordingly, the present invention relates to an organic polymermaterial characterized in that it has a polymer side chain derived froma styrene compound having a haloalkyl group on the benzene ring on thebackbone of an organic polymer base and a functional group capable offorming a complex with a heavy metal ion has been introduced onto saidpolymer side chain. The present invention also relates to a heavy metalion scavenger comprising the organic polymer material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the results of experiments in Example 5performed to compare copper ion scavenging performance of a heavy metalion scavenger comprising an organic polymer material of the presentinvention with those of a commercially available chelate resin and aheavy metal ion scavenger of the prior art.

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

Various aspects of the present invention are explained in detail below.The “functional group capable of forming a complex with a heavy metalion” as defined herein is simply referred to as “chelate group” below.The “styrene compound having a haloalkyl group on the benzene ring” isalso simply referred to as “haloalkyl-substituted styrene” below.

Organic polymer materials of the present invention are chemically verystable because a polymer side chain containing a chelate group has beenintroduced onto the polymer backbone of a chemically stable andsufficiently mechanically strong organic polymer base. They also havethe advantage that no heavy metal ions or reactants are dissipatedbecause the chelate group on the polymer side chain reacts with a heavymetal ion to form a stable complex.

In typical heavy metal ion scavengers comprising chelate resin beads, achelate group has been introduced onto the polymer backbone of a polymerresin to confer heavy metal ion adsorbing function and those polymerbackbones are crosslinked to each other to compensate for deteriorationof physical strength due to introduction of this chelate group. Inchelate resins, a chelate group such as iminodiacetate group has beengenerally introduced onto the backbone of a polystyrene obtained bypolymerizing a styrene monomer. However, once these chelate groups areintroduced, several water molecules are coordinated around the highlyhydrophilic chelate groups to form gaps between polymer chains, wherebythe resin is swollen or otherwise affected to lower the physicalstrength. In order to solve this problem, polystyrene backbones arecrosslinked to each other with a crosslinker such as divinylbenzene inchelate resins. This enhances physical strength of the resins, butanother problem occurs, that is, absorption/desorption functions such asheavy metal ion-absorbing speed or regenerant-diffusing speed arelowered by the formation of a crosslinked structure. In organic polymermaterials of the present invention, a polymer side chain is provided onthe polymer backbone of an organic polymer base and a chelate group isintroduced onto the polymer side chain, whereby excellent heavy metalion adsorbing/desorbing performance can be conferred on the base whilemaintaining the physical strength of the polymer backbone. Heavy metalion scavengers comprising an organic polymer material of the presentinvention can maintain both heavy metal ion-absorbing speed andregenerant-diffusing speed at high level because they have nocrosslinked structure in the polymer backbone. In organic polymermaterials of the present invention, the backbone serves to hold physicalstrength or configuration.

In organic polymer materials of the present invention, suitable meansfor introducing a side chain in the form of a polymer chain onto thepolymer backbone include graft polymerization. Especially,radiation-induced graft polymerization is most preferred for the purposeof the present invention, because a desired graft polymer side chain canbe introduced into an organic polymer base by irradiating the base toproduce a radical and reacting it with a graft monomer and the number orlength of the graft chain can be relatively freely controlled and thepolymer side chain can be introduced into existing polymer materials invarious shapes.

Radiations that can be used in radiation-induced graft polymerizationwell suitable for the purpose of the present invention include α-rays,β-rays, γ-rays, electron rays, UV ray, etc., among which γ-rays andelectron rays are preferred for use in the present invention.Radiation-induced graft polymerization includes preirradiation graftpolymerization involving preliminarily irradiating a graft base and thenbringing it into contact with a polymerizable monomer (graft monomer)for reaction, and simultaneous irradiation graft polymerizationinvolving simultaneously irradiating a system containing a base and amonomer, and either method can be used in the present invention.Radiation-induced graft polymerization includes various manners ofcontact between a monomer and a base, such as liquid phase graftpolymerization performed with a base immersed in a monomer solution, gasphase graft polymerization performed with a base in contact with thevapor of a monomer, or immersion gas phase graft polymerizationperformed by immersing a base in a monomer solution and then removing itfrom the monomer solution for reaction in a gas phase, and any methodcan be used in the present invention.

Fibers and woven/nonwoven fabrics comprising a fiber assembly are themost preferred materials for use as organic polymer bases for preparingorganic polymer materials of the present invention, and are wellsuitable for use in the immersion gas phase graft polymerization becausethey tend to retain monomer solutions.

The functional chelate group capable of forming a complex with a heavymetal ion in organic polymer materials of the present invention can beany one of those known to form a complex with a heavy metal ion in theart, typically functional groups derived from iminodiacetic acid andsodium salts thereof; functional groups derived from various amino acidssuch as phenylalanine, lysine, leucine, valine and proline as well assodium salts thereof; functional groups derived from iminodiethanol,etc.

The polymer side chain introduced onto the polymer backbone of anorganic polymer base in organic polymer materials of the presentinvention is derived from a haloalkyl-substituted styrene. The polymerside chain is introduced by graft-polymerizing a haloalkyl-substitutedstyrene on the backbone of an organic polymer base. An example ofhaloalkyl-substituted styrenes preferred for use in the presentinvention is an halo-n-alkyl-substituted styrene represented by theformula:

Especially preferred are chloromethylstyrene represented by the formula:

and bromoethylstyrene represented by the formula:

Surprisingly, heavy metal ion scavengers comprising an organic polymermaterial having a graft polymer side chain derived from ahaloalkyl-substituted styrene according to the present invention werefound to greatly improve heavy metal ion scavenging performance ascompared with conventional nonwoven materials having a glycidylmethacrylate graft side chain in which the same chelate group has beenintroduced. The reason for this is not unknown, but this is probablybecause the resulting complexes have different stability constants dueto the difference in steric structure between the glycidyl methacrylategraft side chain and the haloalkyl-substituted styrene graft side chain.Previous studies on improvement of ion adsorbing/desorbing performancein this field were solely focused on choice of a chelate group involvedin ion adsorption/desorption and choice of the optimal density, butseldom addressed to the relation between the nature of the graft polymerside chain itself and ion adsorbing/desorbing performance. The presentinvention is the first finding that ion adsorbing/desorbing performanceis influenced by not only choice of a chelate group involved in ionadsorption/desorption and choice of the optimal density but also thenature of the graft polymer side chain.

Organic polymer bases for preparing organic polymer materials of thepresent invention are preferably polyolefin-based organic polymer bases.Polyolefin-based organic polymer bases are suitable for the purpose ofintroducing a graft side chain by radiation-induced graft polymerizationbecause they are not degradable by radiations. Specific examples ofpolyolefin-based polymer materials well suitable for use as organicpolymer bases for preparing organic polymer materials of the presentinvention include, but not limited to, polyolefins such as polyethyleneand polypropylene; halogenated polyolefins such as PTFE and polyvinylchloride; and olefin-halogenated olefin copolymers such asethylene-ethylene tetrafluoride copolymers and ethylene-vinyl alcoholcopolymers (EVA).

These organic polymer bases can be preferably in the form of a polymerelemental fiber or a woven or nonwoven fabric comprising an assemblythereof. Fibrous polymers have a large surface area enough to removeheavy metal ions at high speed and they are light and readily formable.Specific examples of such forms include long fibers and processedproducts thereof, short fibers and processed products thereof as well assegments thereof. Long fibers include, for example, continuousfilaments, and short fibers include, for example, staple fibers.Processed products of long and short fibers include various woven andnonwoven fabrics made from these fibers. Some woven/nonwoven fabricbases have a filter function or the like by themselves so that amultifunctional material can be formed by introducing a chelate groupinto a base having such a function because it can remove not only heavymetal ions but also fine particles or the like. Woven/nonwoven materialscan be suitably used as bases for radiation-induced graftpolymerization, and are preferred for organic polymer materials of thepresent invention used in the form of a filter because they and arelight and easy to form into a filter. Heavy metal ion scavengersprepared from woven/nonwoven fabrics can be easily handled duringdisposal and readily incinerated in contrast to conventional chelateresins having a crosslinked structure that are hard to incinerate.

Organic polymer materials of the present invention can be prepared byfirst introducing a polymer side chain by graft-polymerizing ahaloalkyl-substituted styrene onto the polymer backbone of an organicpolymer base. Then, the halogen group of the polymer side chain can bereplaced with a compound having a chelate group to prepare an organicpolymer material of the present invention. Alternatively, organicpolymer materials of the present invention can also be prepared byreplacing the halogen group of the polymer side chain with a compoundhaving a functional group capable of being converted into a chelategroup and then converting the functional group into the chelate group.Compounds having a functional group capable of being converted into achelate group include, for example, dialkyl iminodiacetate esters andalkyl esters of various amino acids. Specifically, chloromethylstyreneis first graft-polymerized onto the polymer backbone of an organicpolymer base and the chloro group on the resulting polymer side chainreacted with a sulfide to form a sulfonium salt, which is then reactedwith sodium iminodiacetate, whereby an organic polymer material of thepresent invention in which a sodium iminodiacetate group has beenintroduced onto the polymer side chain can be obtained. Alternatively,chloromethylstyrene is first graft-polymerized onto the polymer backboneof an organic polymer base and the chloro group on the resulting polymerside chain is replaced with iodine and then reacted with diethyliminodiacetate ester to replace iodine with a diethyl iminodiacetateester group, which is then converted into a sodium salt by reaction withsodium hydroxide, whereby an organic polymer material of the presentinvention in which a sodium iminodiacetate group has been introducedonto the polymer side chain can be obtained.

Heavy metal ion scavengers comprising an organic polymer material of thepresent invention can be suitably used to remove heavy metal ions in notonly water but also organic media by selecting the nature of the chelategroup. For example, the inventors found that heavy metal ion scavengershaving a chelate group derived from iminodiethanol show more excellentheavy metal ion scavenging performance in organic media than thosehaving an iminodiacetate group.

Heavy metal ion scavengers comprising an organic polymer material of thepresent invention can be used to remove various heavy metal ions. Heavymetal ions that can be removed by heavy metal ion scavengers of thepresent invention include cobalt, nickel, copper, mercury, cadmium,lead, iron, zinc or the like.

The following examples illustrate various specific embodiments of thepresent invention without, however, limiting the invention thereto.

EXAMPLE 1

A nonwoven cloth having an areal density of 50 g/m² made of apolyethylene fiber of about 10-16 μm in diameter was used as an organicpolymer base. This nonwoven cloth base in an amount of 40 g wasirradiated with γ-rays at 160 kGy with cooling on dry ice. Thisirradiated base was immersed in chloromethylstyrene (50% m-isomer, 50%p-isomer, trade name: CMS-AM from Seimi Chemical) preliminarily freed ofpolymerization inhibitors and reacted at 50° C. for 5 hours to give 86 gof a chloromethylstyrene-grafted nonwoven cloth at a grafting degree of115%.

This grafted nonwoven cloth in an amount of 19.6 g was immersed in asolution of 52.5 g iminodiethanol in isopropyl alcohol (450 ml) andreacted at 70° C. for 48 hours. After reaction, the nonwoven cloth basewas successively washed with pure water, 0.1 N aqueous sodium hydroxidesolution and methanol, and then the solvent was wiped off and the basewas dried under reduced pressure at 50° C. for 12 hours to give 23.7 gof an organic polymer material of the present invention. This isdesignated as heavy metal ion scavenger 1.

EXAMPLE 2

A chloromethylstyrene-grafted nonwoven cloth in an amount of 20.7 gobtained in the same manner as in Example 1 was immersed in a solutionof 36 g sodium iodide in acetone (400 ml) and reacted at 50° C. for 48hours. After reaction, the nonwoven cloth base was successively washedwith pure water and acetone, and then the solvent was wiped off. Then,this nonwoven cloth was immersed in a solution of 77.8 g diethyliminodiacetate in dimethylformamide (360 ml) and reacted at 80° C. for48 hours. After reaction, the nonwoven cloth was washed with methanol.This nonwoven cloth was further immersed in 1N sodium hydroxide-ethanolmixed solution (200 ml+200 ml) and reacted at 80° C. for 48 hours andthen repeatedly washed with pure water, and then water was wiped off andthe nonwoven cloth was dried under reduced pressure at 50° C. to give28.5 g of an organic polymer material of the present invention. This isdesignated as heavy metal ion scavenger 2.

COMPARATIVE EXAMPLE 1

In the same manner as in Example 1, 11.5 g of a nonwoven polyethylenecloth was irradiated with γ-rays. This was immersed in glycidylmethacrylate and subjected to graft polymerization at 60° C. for 3hours, to give 23.0 g of a glycidyl methacrylate-grafted nonwoven clothat a grafting degree of 100%.

This grafted nonwoven cloth in an amount of 8.0 g was immersed in asolution of 13 g sodium iminodiacetate in water-isopropanol (85 ml+85ml) and heated at 80° C. for 24 hours. After reaction, the nonwovencloth was successively washed with pure water, 0.2 N NaOH and purewater, and then the solvent was wiped off and the nonwoven cloth wasdried under reduced pressure at 50° C. to give 11.1 g of heavy metal ionscavenger A.

EXAMPLE 3 Evaluation Tests for Copper ion Scavenging Performance ofHeavy Metal Ion Scavengers in Water (Batch Tests)

An aqueous solution at 100 ppm copper ion (pH=5.15) was prepared bydissolving copper sulfate in pure water. In an Erlenmeyer flask equippedwith a stopper, a 9 cm² sample of each of heavy metal ion scavengers 2and A obtained above was immersed in 100 ml of this aqueous solution andslowly stirred at 25° C. The copper ion level in the aqueous solutionwas determined 5, 15, 30, 60 and 120 minutes after the scavenger wasimmersed. The results are shown in Table 1 below.

TABLE 1 Scavenger 2 Scavenger A Weight of scavenger (mg) 168.4 191.2Copper ion level (ppm) After 5 minutes 31.4 37.0 After 15 minutes 8.7515.4 After 30 minutes 0.6 6.9 After 60 minutes 0.13 1.0 After 120minutes 0.09 0.6

Table 1 shows that a heavy metal ion scavenger comprising an organicpolymer material of the present invention has remarkably excellentcopper ion scavenging performance as compared with a conventionalscavenger obtained by grafting glycidyl methacrylate.

EXAMPLE 4 Evaluation Tests for Copper Ion Scavenging Performance ofHeavy Metal Ion Scavengers in an Organic Medium (Batch Tests)

An isopropyl alcohol solution at 5 ppm copper ion was prepared by adding0.5 ml of an aqueous solution at 1000 ppm copper sulfate to 100 ml ofisopropyl alcohol. In an Erlenmeyer flask equipped with a stopper, a 20cm² sample of each of heavy metal ion scavengers 1 and 2 obtained abovewas immersed in 100 ml of this solution and slowly stirred at 25° C. Thecopper ion level in the solution was determined 1, 2, 6 and 24 hoursafter the scavenger was immersed. The results are shown in Table 2below.

TABLE 2 Scavenger 1 Scavenger 2 Weight of scavenger (mg) 341.1 357.3Copper ion level (ppm) After 1 hour 3.02 4.16 After 2 hours 2.14 4.10After 6 hours 0.55 4.08 After 24 hours 0.10 4.07

Table 2 shows that scavenger 1 (having an iminodiethanol chelate group)has more excellent copper ion scavenging performance in an organicmedium than scavenger 2 (that showed excellent copper ion scavengingperformance in water).

EXAMPLE 5 Evaluation Tests for Copper Ion Scavenging Performance ofScavengers (Continuous Tests)

A stack of samples of 18 mm in diameter of heavy metal ion scavenger 2or A obtained above or a commercially available chelate resin (DIAIONCR11) were packed in a glass column having an inner diameter of 18 mm upto a bed height of 2.2 cm (bed volume 5.1 ml). This column waspretreated by passing 2 L of pure water at a flow rate of 1.27 L/h forheavy metal ion scavengers 2 and A or 0.13 L/h for DIAION. Then, anaqueous solution at 10 ppm copper ion (pH=5.4) was passed at a flow rateof 1.27 L/h (SV=250/h) and copper ion levels in treated water weredetermined. The results are shown in FIG. 1.

FIG. 1 shows that a heavy metal ion scavenger comprising an organicpolymer material of the present invention more effectively retainscopper ion scavenging performance than either a commercially availablechelate resin or a conventional heavy metal ion scavenger based onglycidyl methacrylate. Moreover, copper ion can be effectively removedeven at a very high flow rate as shown in this example, suggesting thepossibility of greatly reduced process time and space saving in heavymetal removal.

INDUSTRIAL APPLICABILITY

Organic polymer materials of the present invention are characterized inthat they have a polymer side chain derived from a haloalkyl-substitutedstyrene on the backbone of an organic polymer base and a chelate grouphas been introduced onto the polymer side chain, and therefore, thesematerials can attain more excellent heavy metal ion adsorbing/desorbingperformance and can be suitably used as heavy metal ion scavengersbecause they have high physical strength and rapidly adsorb/desorb heavymetal ions and diffuse regenerants. Especially, they have greatlyimproved heavy metal ion scavenging performance as compared withconventional heavy metal ion scavengers having a glycidylmethacrylate-grafted side chain. They can be safely used againstenvironmental pollution without incidentally releasing adsorbed heavymetal ions because heavy metal ions are stably coordinated to thechelate group directly linked to the polymer base via covalent bond.Spent scavengers can be reused because they can be regenerated with analkali after dissolution of heavy metal ions with an acid. Heavy metalion scavengers of the present invention are readily disposable byincineration or other means and lighter and less expensive as comparedwith conventional chelate resins. Heavy metal ion scavengers comprisingan organic polymer material of the present invention can be used toeffectively remove heavy metal ions in not only water but also organicmedia by suitably selecting the chelate group. The amount of the chelategroup, the diameter of the fiber and other factors of heavy metal ionscavengers of the present invention can be appropriately selecteddepending on conditions such as temperature, concentration and scalebecause they comprise a readily formable and compact polymer material.

The present invention includes the following aspects.

1. An organic polymer material characterized in that it has a polymerside chain derived from a styrene compound having a haloalkyl group onthe benzene ring on the backbone of an organic polymer base and afunctional group capable of forming a complex with a heavy metal ion hasbeen introduced onto said polymer side chain.

2. The organic polymer material as defined in 1 above wherein saidorganic polymer base comprises a polyolefin-based organic polymer.

3. The organic polymer material as defined in 1 or 2 wherein saidorganic polymer base has a form selected from fibers, woven or nonwovenfabrics comprising a fiber assembly and processed products thereof andsegments thereof.

4. The organic polymer material as defined in any one of 1 to 3 whereinsaid polymer side chain has been introduced onto the backbone of anorganic polymer base by radiation-induced graft polymerization.

5. The organic polymer material as defined in any one of 1 to 4 whereinsaid functional group capable of forming a complex with a heavy metalion is a group derived from iminodiacetic acid, iminodiethanol, aminoacids or a salt thereof.

6. A heavy metal ion scavenger comprising the organic polymer materialas defined in any one of 1 to 5.

7. A process for preparing the organic polymer material as defined inany one of 1 to 5, comprising graft-polymerizing a styrene compoundhaving a haloalkyl group on the benzene ring to an organic polymer baseto form a polymer side chain and then introducing a functional groupcapable of forming a complex with a heavy metal ion onto said polymerside chain by reacting said polymer side chain with a compound havingsaid functional group capable of forming a complex with a heavy metalion or reacting said polymer side chain with a compound having a groupcapable of being converted into said functional group and thenconverting said group into said functional group.

1. An organic polymer material having a polymer side chain derived from a styrene compound having a haloalkyl group on the benzene ring on the backbone of an organic polymer base and a functional group capable of forming a complex with a heavy metal ion which has been introduced onto said polymer side chain.
 2. The organic polymer material as defined in claim 1 wherein said polymer side chain has been introduced onto the backbone of an organic polymer base by radiation-induced graft polymerization.
 3. The organic polymer material as defined in claim 1 wherein said functional group capable of forming a complex with a heavy metal ion is a group derived from iminodiacetic acid, iminodiethanol, amino acids or a salt thereof.
 4. A heavy metal ion scavenger comprising the organic polymer material as defined in claim
 1. 5. A process for preparing the organic polymer material as defined in claim 1, comprising graft-polymerizing a styrene compound having a haloalkyl group on the benzene ring to an organic polymer base to form a polymer side chain and then introducing a functional group capable of forming a complex with a heavy metal ion onto said polymer side chain by reacting said polymer side chain with a compound having said functional group capable of forming a complex with a heavy metal ion or reacting said polymer side chain with a compound having a group capable of being converted into said functional group and then converting said group into said functional group. 